The present disclosure relates to a method for producing a component, in particular a rotor wheel, to a component, in particular a rotor wheel, to a method for producing a component composite, in particular a rotor, and also to a component composite, in particular a rotor.
For modern internal combustion engines, use is increasingly being made of exhaust-gas turbochargers, in order to realize considerably more economical and nevertheless dynamic and convenient diesel and petrol engines. Nickel (Ni) base alloys are used at present as the material for the exhaust-gas-side turbine wheel. To improve the dynamics, alloys based on titanium aluminides (TiAl) are increasingly coming into consideration, these being distinguished by a low density (˜4 g/cm3) and a high specific strength. Turbine wheels made of TiAl base alloys can be produced, for example, by investment casting methods or metal injection molding (MIM). A major challenge is to attach the TiAl turbine wheel to the steel shaft, which connects the turbine wheel to the compressor wheel on the air side.
Fusion welding methods, e.g. electron or laser beam welding, are currently the established way of joining turbine wheels made of Ni base alloys to the steel shaft on account of a short cycle time and a high reliability of the joint. However, the pronounced formation of brittle phases between Ti, Fe and Al prevents these welding methods from being transferred for joining turbine wheels made of TiAl base alloys to steel.
To solve this problem, it is possible for intermediate pieces which are made of Ni base alloys and which can be welded to steel to be attached to the TiAl turbine wheel, e.g. by diffusion welding or friction welding. However, these approaches are time-consuming and costly. Furthermore, an intermediate layer which is made of an Ni base alloy and which can be welded to steel can be applied by powder spraying methods, e.g. by plasma spraying, high-velocity flame spraying or cold spraying. These methods are likewise costly and utilize the expensive powders used only to a small extent. In addition, no metallurgical connection is made between the TiAl base alloy and the intermediate layer made of an Ni base alloy in these methods. It is not possible to attach the intermediate layer made of an Ni base alloy to the TiAl turbine wheel by co-sintering on account of the various melting ranges of TiAl and Ni base alloys and the high tendency of Ni base alloys to react with TiAl base alloys.
DE 10 2010 011 486 A1 describes an exhaust-gas turbocharger which, in order to attach the turbine wheel to the shaft, has, at least between said turbine wheel and the shaft, at least one porous metallic or ceramic intermediate piece connected to the turbine wheel and/or the shaft by way of an infiltration process.